The arylalkyl amines, in particular benzylamine and dibenzylamine are important industrial organic compounds. Benzylamine is a primary amine which is useful as a corrosion inhibitor. Dibenzylamine is a secondary amine which finds use in the production of synthetic penicillins and in the vulcanization of rubber.
Numerous procedures for the production of these amines are described in the literature and include: the reductive amination of benzaldehyde by hydrogen and ammonia in the presence of a catalyst; the catalytic reduction of benzonitrile or benzylhydroxylamine; or the condensation of benzaldehyde and benzylamine followed by catalytic hydrogenation of the intermediate Schiff's base. Generally, benzylamine and dibenzylamine are obtained in poor yield and each amine must be carefully separated from mixtures containing primary, secondary or tertiary amines, imines, aldehydes, alcohols or amides to obtain a high purity product.
For example, it is known that nitriles can be catalytically reduced to the primary amine through the intermediate imine by a wide variety of catalysts as follows: EQU RC.tbd.N+H.sub.2 .fwdarw.RCH.dbd.NH+H.sub.2 .fwdarw.RCH.sub.2 NH.sub.2
the intermediate imine further reacts with the primary amine to produce a Schiff's base with the liberation of ammonia, EQU RCH.dbd.NH+RCH.sub.2 NH.sub.2 .revreaction.RCH.dbd.NCH.sub.2 R+NH.sub.3 .uparw.
In the presence of a catalyst and hydrogen, the Schiff's base is further reduced to the secondary amine, EQU RCH.dbd.NCH.sub.2 R+H.sub.2 .fwdarw.(RCH.sub.2).sub.2 NH
in a batch process, the above reactions compete for reactants and a variety of reaction products are formed. Many means have been employed to minimize the extent of these reactions including reduction in very dilute organic solvent solutions, solvent selection and catalyst selection. Rylander et al. disclose, in U.S. Pat. No. 3,117,162 and Annals N.Y. Acad. Sci. 214:100-109(1973), a batch process for the reduction of benzonitrile in dilute organic solvent solutions such as hexane, octane, ethanol and benzene by hydrogenation over rhodium, palladium, platinum, or ruthenium catalysts (all 5% on carbon). At best, Rylander et al. obtain benzylamine at 63% yield from a mixed reaction product containing 34% of the secondary amine. The production of dibenzylamine is favored in this process by the selective use of rhodium on carbon or platinum on carbon catalysts, but in all other cases it is obtained as a mixture containing large amounts of the primary amine. In addition, long reaction times, 2 to 21 hours, are required to reduce the benzonitrile and the reaction products must be further separated from very dilute organic solvent solutions. Similarly, Takagi et al. in Sci. Papers Inst. Phys. Chem. Res. 61(3), 114-117(1967), disclose a batch process for the reduction of benzonitrile in ethanol over 3:1 iridium platinum oxide catalyst. This reaction produces about 42% benzylamine and 50% dibenzylamine. In each case long reaction times are required and the reaction products must be separated from very dilute solutions. As a result, these prior art techniques are time consuming and costly.